Film control in motion picture projectors

ABSTRACT

In one embodiment, a motion picture projector includes a film supply reel, an upper shuttle loop sprocket, a gate assembly which includes a frame-by-frame film advance mechanism, a lower shuttle loop sprocket, and a film takeup reel; these projector components are disposed serially along a film path which traverses an optical axis within a shuttle loop defined between the sprockets. The reels are of very large capacity and have substantial inertia when fully or even partially loaded. In this context, the invention provides mechanisms for controlling film tension at the sprockets to preserve the film and the definition of the shuttle loop. A tension control mechanism is located nextadjacent each sprocket along the film path toward the adjacent reel. Each mechanism is operative, when the adjacent sprocket operates to feed film to the shuttle loop, to feed film to the sprocket at a rate greater than the sprocket film advance rate when the film tension in the path adjacent the mechanism exceeds a predetermined film tension level. The control mechanism adjacent the upper shuttle loop sprocket also functions, when that sprocket operates to extract film from the shuttle loop, to retard the rate at which film is taken from the upper sprocket in response to the presence in the adjacent film of a tension level in excess of a predetermined level. Film handling apparatus is provided for the film within the shuttle loop and is operatively disengaged from the film during operation of the projector to display a film. During rewind and stand-by modes of projector operation, the film handling apparatus is operatively engaged with the film to define a film path between the sprockets which is of definite length. This apparatus includes means for disabling the frame-by-frame film advance mechanism when the apparatus is disposed to define the length of film between the sprockets.

United States Patent [19] Henderson 51 Nov. 20, 1973 James B. Henderson,Monrovia, Calif.

[73] Assignee: Bell & Howell Company, Chicago,

Ill.

[22] Filed: Oct. 16, 1972 [21] Appl. No.: 297,749

Related U.S. Application Data [63] Continuation-in-part of Ser. No.211,021, Dec. 22,

1971, Pat. NO. 3,748,030.

[75] Inventor:

Primary ExaminerSamuel S. Matthews Assistant Examiner-Michael L. GellnerAttorneyRobert L. Parker et al.

[5 7] ABSTRACT In one embodiment, a motion picture projector includes afilm supply reel, an upper shuttle loop sprocket, a gate assembly whichincludes a frame-byframe film advance mechanism, a lower shuttle loopsprocket, and a film takeup reel; these projector components aredisposed serially along a film path which traverses an optical axiswithin a shuttle loop defined between the sprockets. The reels are ofvery large capacity and have substantial inertia when fully or evenpartially loaded.

In this context, the invention provides mechanisms for controlling filmtension at the sprockets to preserve the film and the definition of theshuttle loop. A tension control mechanism is located nextadjacent eachsprocket along the film path toward the adjacent reel. Each mechanism isoperative, when the adjacent sprocket operates to feed film to theshuttle loop, to feed film to the sprocket at a rate greater than thesprocket film advance rate when the film tension in the path adjacentthe mechanism exceeds a predetermined film tension level. The controlmechanism adjacent the upper shuttle loop sprocket also functions, whenthat sprocket operates to extract film from the shuttle loop, to retardthe rate at which film is taken from the upper sprocket in response tothe presence in the adjacent film of a tension level in excess of apredetermined level.

Film handling apparatus is provided for the film within the shuttle loopand is operatively disengaged from the film during operation of theprojector to display a film. During rewind and stand-by modes ofprojector operation, the film handling apparatus is operatively engagedwith the film to define a film path between the sprockets which is ofdefinite length. This apparatus includes means for disabling theframe-by-frame film advance mechanism when the apparatus is disposed todefine the length of film between the sprockets.

18 Claims, 9 Drawing Figures United States Patent 1 [111 3,773,411

Henderson Nov. 20, 1973 PATENTED NOV 20 I975 SHEET 4 [IF 5 m nnow v20 ms3,773.41 1

SHEET 5 or 5 FILM CONTROL IN MOTION PICTURE PROJECTORS RELATED PATENTAPPLICATIONS This application is a continuation-in-part of applicationSer. No. 211,021, filed Dec. 22, 1971, now U.S. Patent No. 3,748,030.

INCORPORATION BY REFERENCE The description of this inventionincorporates by reference the drawings and description of commonlyownedU.S. Pat. No. 3,201,020 issued Aug. 17, 1965 to J. Cherniavskyj et alfor Self-Threading Motion Picture Projector. Thisincorporation-by-reference is for the purposes of simplifying thedrawings and descriptions of this invention, and also for the purpose ofproviding a clear and concise description of this invention.

The presently preferred embodiments of this invention illustrated anddescribed herein are based upon and constitute modifications ofprojectors constructed as described in U.S. Pat. No. 3,201,020. It issuggested that U.S. Pat. No. 3,201,020 be read before or in conjunctionwith a reading of the following detailed description of this inventionfor best understanding of the structures and operation of thisinvention, and of how projectors according to this invention may beconstructed to advantage.

In the accompanying drawings and description, reference numerals between1 and 116, inclusive, refer to structure which is illustrated anddescribed in U.S. Pat. No. 3,201,020, whereas reference numerals 120 andhigher refer to structures provided in accord with the presentinvention.

FIELD OF THE INVENTION This invention pertains to film handling and filmtension control in motion picture projectors.

BACKGROUND OF THE INVENTION The Prior Art and Its Problems Practicallyall motion picture projectors are arranged to provide a shuttle loop inthe film path across the optical (projection) axis. A shuttle loop isrequired because the actual movement of the film across the optical axismust be on a frame-by-frame basis, whereas film is supplied to andextracted from the shuttle loop on a continuous basis by sprocket wheelsat the ends of the shuttle loop. The sprocket wheels carry teeth whichcooperate in sprocket holes formed in the film along one or both marginsof the film. In order that the projector may function properly, the netfilm advance rate past the optical axis (on a frame-by-frame basis at 24frames per second, in the case of 16 mm. film) and the net rate of filmmovement into and out of the shuttle loop continuously by the sprocketsmust be equal.

The familiar effect of frame jump or chatter is a result of filmsprocket hole mutilation. A significant cause of sprocket holemutilation in motion picture film is excess tension in the film adjacentthe sprockets outside the shuttle loop. If the film tension is too high,the sprockets may lose a frame on the film, i.e., the sprocket at theinput end of the shuttle loop may pass only 23 or less frames of film tothe shuttle loop in any given second, or the sprocket at the exit end ofthe loop may allow 25 or more frames to be pulled from the shuttle loop.The tendency of a sprocket to lose a frame increases as the tension inthe film adjacent the sprocket increases. Also, if any sprocket holes inthe film have been mutilated (e.g., elongated) or destroyed (a result,principally, of excess film tension), then the tendency of the sprocketto lose a frame is greatly increased.

ln motion picture projectors adapted for home use and the like,operational simplicity of the projector and considerations of cost argueagainst the provision of mechanisms for regulating film tension adjacentthe shuttle loop sprockets. Projectors for conventional theaters and thelike need not be simple to operate because they are operated by skilledprofessional projectionists, nor need they be portable; accordingly,large, heavy-use projectors for conventional theaters and the like mayand often do include film tension control devices which greatlycomplicate the task of threading the film into the projector.

U.S. Pat. No. 3,617,117, for example, describes a motion pictureprojection system adapted for use in commercial aircraft and in whichreels of great capacity are used; these reels may be thirty inches ormore in diameter. To enable use of the system in aircraft,

weight must be conserved in the system wherever possible; systemsconstructed to date in accord with U.S. Pat. No. 3,617,117, therefore,used modified forms of 16 mm. projectors designed for home use,specifically Bell & Howell Series 500 projectors.

The unusually large film reels found in systems in accord with U.S. Pat.No. 3,6l7,1 l7 possess considerable inertia when loaded. Thus, eventhough these reels may be fitted with special tension sensitive drivemechanisms, they often produce considerable tension in the film adjacentthe shuttle loop sprockets, thereby rendering the projectors susceptibleto the familiar problem of frame jump. Because of the projectors in suchsystems are located in relatively inaccessible places in the aircraft,the problem of frame jump, once encountered, cannot readily becorrected.

It is apparent, therefore, that a need exists for simple compact andeffective structure, useful in the context of a motion picture projectordesigned for home use and the like, for controlling the tension in filmadjacent the shuttle loop sprockets and for maintaining film tension inthis area within acceptable low levels.

The rewinding of film in a home projector conventionally is accomplishedindependently of the mechanisms used to move film through the projectorduring showing of a movie. That is, in a projector designed for homeuse, film is rewound by threading film directly from the filled takeupreel to the empty supply reel, and by powering the supply reel to windin film from the takeup reel. The system of U.S. Pat. No. 3,617,117,however, relies upon the movement of film from the takeup reel to thesupply reel along the same film path as is used during display of thefilm. This manner of rewinding of the film subjects the film to handlingby the frame-by-frame advance mechanism of the projector which, by itsnature, can destroy film sprocket holes if a frame is lost from theshuttle loop. Frame-by-frame forward advance of film within the shuttleloop is essential to intelligible display of the film, but frame-byframemovement of the film during reverse (rewind) mode operation is only asource of potential mutilation or destruction of the film. Thus, a needexists for apparatus responsive to reverse mode operation of a projectoradapted for home use for effectively disabling the frame-by-frame filmadvance mechanism.

3 U.S. Pat. No. 3,6l7,l 17 has been mentioned above primarily becausethis patent shows an environment in which the improvements of thisinvention have utility. Workers skilled in the art and science of motionpicture projectors will readily appreciate that this invention hasutility in projection systems apart from those arranged for use in thepassenger spaces of commercial aircraft. For example, projection systemsincorporating large film storage reels may be used in small or one-mantheaters. Such projection systems have large film storage capacity sothat one man may perform the functions of projectionist, ticketsalesman, and popcorn vendor. To be useful in such areas, the projectorshould be easy to thread and require no monitoring during operation todisplay a film. The tension controlling features of this invention areuseful in such projection systems, especially where the projectormechanism is in large part one designed for home use.

SUMMARY OF THE INVENTION This invention provides simple, effective,compact and reliable apparatus for controlling film tension in aprojector adjacent the shuttle loop sprockets to eliminate the tendencyof the sprockets to lose a frame. Because the apparatus is compact, itmay be used to advantage in projectors originally designed for home useand the like. Also, this invention provides apparatus for disabling theframe-by-frame film advance mechanism of a projector when the projectoris operated in reverse mode for rewinding film, for example. Thus, thisinven' tion may be used to enhance the reliability of projection systemsembodying the invention of U.S. Pat. No. 3,6l7,l 17, for example, aswell as other projection systems whether or not they use very largecapacity film storage reels.

Generally speaking, this invention is provided in the context of amotion picture projector which includes a film supply reel, an uppershuttle loop sprocket, a gate assembly which includes a frame-by-framefilm advance mechanism, a lower shuttle loop sprocket, and a film takeupreel; these components are arranged serially along a film path whichtraverses a projector optical axis within a shuttle loop between thesprockets. In this context, this invention provides film control meansdisposed along the film path nextadjacent one of the sprockets towardthe adjacent reel. The control means is operative in response to a filmtension level in excess ofa predetermined tension level in the adjacentfilm for driving film toward the sprocket at a rate which is greaterthan the rate of film advance by the one sprocket.

Also, in this context, this invention provides means responsive toreverse mode operation of the projector for disabling the frame-by-frameadvance mechanism from effective advancing cooperation with the filmpath.

In a modified version of the projector, the film passes directly fromthe film tensioning means into the film advance mechanism without anyintermediate sprocket drive. The film tensioning mechanism provides abuffering means between the supply reel and the intermittent movement ofthe film through the drive mechanism, thus eliminating the need for thesprocket drive to move the film and maintain the shuttle loop.

DESCRIPTION OF THE DRAWINGS The above-mentioned and other features ofthis invention are more fully set forth in the following description ofpresently preferred embodiments of the invention, which description ispresented with reference to the drawings of U.S. Pat. No. 3,201,020which are incorporated by reference herein, and by reference to theaccompanying drawings wherein:

FIG. 1 is an elevation view, with parts broken away, of the projectionstation in a projection system according to this invention;

FIG. 2 is a view taken along lines 2-2 in FIG. 1;

FIG. 3 is a view taken along lines 33 in FIG. 1;

FIG. 4 is a cross-sectional elevation view of another film tensioncontrolling mechanism for use with the upper shuttle loop sprocket inthe projector station shown in FIG. 1;

FIG. 5 is a schematic view of a portion of the drive mechanism for theprojector station shown in FIG. 1;

FIG. 6 is a fragmentary rear elevation view of a portion of theprojection station shown in FIG. 1;

FIG. 7 is an enlarged fragmentary elevation view of another form oftight-loop rewind mechanism for the projection station shown in FIG. 1;

FIG. 8 is a cross-sectional view taken along lines 88 in FIG. 7; and

FIG. 9 is an elevational view of a modified projection systemincorporating the features of the invention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS The drawings and descriptionsof U.S. Pat. No. 3,201 ,020 are incorporated herein by reference asthough fully set forth at this point. The structures illustrated in U.S.Pat. No. 3,201,020 form the presently preferred environment within whichthe improvements provided by the present invention are defined.

A comparison of accompanying FIG. 1 with FIG. 2 of U.S. Pat. No.3,201,020 shows that the improvements provided by this invention mayadvantageously rely upon and incorporate substantial portions of thestructure described in the referenced patent. Thus, as shown inaccompanying FIG. 1, a projection station is provided in an overallprojection system which includes large diameter film supply and takeupreels (not shown, but see U.S. Pat. No. 3,617,117, for example). Film 7is led from the supply reel to projection station 120 to pass in serialorder through an upper film tension controlling mechanism 121 aroundupper shuttle loop sprocket 24, through gate assembly 34, around theupper portion of lower shuttle loop sprocket 74, around a sound drum103, then around other portions of the lower shuttle loop sprocket,through a lower film tension controlling mechanism 122, and thence viasuitable film guides and the like (not shown) to the film takeup reel.The portion of film 7 lying along the above-described path between uppershuttle loop sprocket 24 and the upper portions of lower shuttle loopsprocket 74 are disposed in that portion 123 of the film path which iscommonly referred to as the shuttle loop. In accompanying FIG. 1, themechanism of projection station 120 during reverse mode operation isshown in solid lines.

Sprockets 24 and 74 are essentially identical and are driven at equalrates in opposite directions in a continuous manner during operation ofthe projection station. Sprockts 24 and 74 are secured to sprocket driveshafts 25 and 47, respectively, adjacent the front face of projectorhousing 12. Adjacent the rear face of the housing, however, shafts and47 are secured to pinion gears 124 and 125, respectively, whichcooperate with a worm gear 126 affixed to projector drive shaft 100which is in turn driven by a projector drive motor 127 (see accompanyingFIG. 5).

During forward mode operation of projector station 120, upper shuttleloop sprocket 24 functions to continuously feed film 7 into shuttle loop123 at a rate of 24 frames per second (in the case of l6 mm. film, forexample), and lower sprocket 74 functions to extract film from theshuttle loop continuously at a rate of 24 frames per second; duringreverse mode operation of the projection station, the functions ofsprockets 24 and 74 are reversed. Within the shuttle loop, aconventional pull-down mechanism operates during forward mode operationof the projection station to advance film within the shuttle loop towardlower sprocket 74 on a frame-by-frame basis at a rate of 24 frames persecond. During reverse mode operation of the projection station, thepull-down mechanism (not illustrated in the accompanying drawings, butsee FIGS. 4, 5 and 6 of US. Pat. No. 3,201,020) would advance film alongthe shuttle loop discontinuously on a frame-by-frame basis but for theoperation of tight-loop rewind mechanism 200 described below.

Correct operation of projection station 120 is dependent upon therebeing a predetermined amount of film within the shuttle loop at alltimes. It is preferred that the improvements of this invention beprovided in the context of a Series 500 Bell & Howell motion pictureprojector; such projectors are constructed for handling 16 mm. film, andin such projectors it is preferred that the quantity of film definingshuttle loop 123 correspond to 27 consecutive frames of the 16 mm. film.It is also preferred that the film within the shuttle loop bedistributed within the shuttle loop with approximately half the lengthof the shuttle loop being disposed above the optical axis 128, andapproximately half the length of the shuttle loop being disposed belowthe optical axis adjacent lower shuttle loop sprocket 74. The desireddistribution of film within the shuttle loop cannot be maintained if thesprocket holes in the film 7 are mutilated or destroyed such that teeth88 on the shuttle 87 of the pull-down mechanism cannot properly engagethe film. Similarly, sprockets 24 and 74 cannot function correctly tofeed film to the shuttle loop and to extract film from the shuttle loopat the rate of 24 frames during each second of operation of theprojector if the film sprockets holes are mutilated or destroyed suchthat the circumferential teeth 129 (see accompanying FIG.

I 8) on the sprockets cannot properly engage the film. It

is apparent, therefore, that the presence of mutilated or destroyedsprocket holes in film 7 renders the projector susceptible tomalfunction during the display of a program defined by film 7. To theextent that the film is under undesired levels of tension adjacentsprockets 24 and 74 and the film carries mutilated or destroyed sprocketholes, then it is apparent that the likelihood exists that one or bothof the sprockets may lose a frame relative to the film and feed lessfilm than is desired, or extract more film than is desired, from theshuttle loop during each second of operation of the projector. Thus, theefficient and reliable operation of projection station 120 is in largemeasure dependent upon film 7 being free of destroyed or multilatedsprocket holes.

Multilation or destruction of the sprocket holes of film 7 is producedin many cases by there being too great a level of tension present in thefilm as it approaches or leaves the shuttle loop via sprockets 24 and 74during forward or reverse mode operation of the projector. It isapparent, therefore, that it is desirable that the film, in thoseportions of the film path through projection station lying adjacent tosprockets 24 and 74 and outside of shuttle loop 123, be at acceptablelow tension levels if sprocket hole mutilation or destruction is to beavoided, film tension controlling mechanism 121 and 122 are provided inprojection station 120 to assure that film 7 is presented to and ledfrom sprockets 24 and 74 at safe tension levels during operation of theprojection station. The provision of control mechanism 121 and 122 isparticularly desirable where the film supply and takeup reels are ofgreatly increased capacity and thereby possess considerable angularinertia, as is the case where projection station 120 is provided in thecontext of the projection system described in US. Pat. No. 3,6l7,l 17,for example.

As shown in accompanying FIGS. 1 and 2, a puck drum 130, equipped with acircumferential rubber tire 131, is secured to a shaft 132 which isdisposed parallel to drive shaft 25 for upper shuttle loop sprocket 24.Shaft 132 is disposed adjacent the path of film 7 between sprocket 24and the film supply reel closely adjacent to the upper sprocket. Shaft132 is rotatably mounted within a bearing block 133 by suitable bearings134. The bearing block is affixed to frame plate 2 adjacent the front ofprojector housing 12. Bearing block 134 is sized so that puck drum andthe other rollers and rolls of control mechanism 121 are spaced the samedistance from frame plate 2 as sprockets 24 and 74; thus, the film paththrough projection station 120 lies in a common plane within whichoptical axis 128 is also disposed.

A drive arm 135 is pivoted to bearing block 134 by a pivot shaft 136carried by a support bracket 137 secured to the bearing block. Pivotshaft 136 is parallel to shaft 132 so that drive arm 135 is pivotableabout shaft 136 in a plane perpendicular to shaft 132. An'

idler roller 138 is rotatably mounted to a lower end 139 of the drivearm 135. A pinch roller 140 is carried by drive arm 135 between pivot136 and idler roller 138. The shaft 141 for the pinch roller is carriedby the drive arm very close to pivot 136. Accordingly, drive arm 135manifests a large mechanical advantage in response to forces applied tothe drive arm via idler roller 138. Clockwise movement of the drive armabout its pivot moves pinch roller 140 toward engagement with theadjacent surface of puck tire 131. Drive arm 135 is biased to rotatecounterclockwise about pivot 136 by a return spring 142 which is coupledbetween the drive arm at about its midlength and a lug 143 extended appropriately from bearing block 134. An idler carrier plate 144 ismounted to the bearing block and extends generally along the film pathin a direction toward the supply reel from the puck. An idler roller 145is rotatably mounted to the carrier plate for rotation about an axisparallel to and spaced from puck shaft 132. A keeper roller 146 isrotatably mounted to the carrier plate adjacent idler roller 145.

As shown in accompanying FIG. 1, the desired path through projectionstation 120 to upper shuttle loop sprocket 24 is first between idlerroller 145 and keeper roller 146 from the supply reel, then betweenpinch roll 140 and the periphery of puck tire 131, and then around asubstantial portion of the circumference of idler roller 138 to guideroll 27 associated with sprocket 24. The definition of the film path inthe vicinity of control mechanism 121 is such that the included anglebetween the legs of the film path adjacent idler roller 138 (i.e.,between pinch roller 140 and roller 138 and between guide roll 27 androller 138) is an acute angle, and the pivot axis 136 for the drive armis outside this included angle. Accordingly, drive arm 135 is sensitiveto the tension in film 7 between idler roller 138 and sprocket 24, aswell as between the idler roller 145 and the pinch roller 140.

Spring 142 is selected so that, when film 7 is subjected to tensionbetween idler roller 138 and sprocket 27 at a level equal to or lessthan a tension level established as being adequate to assure thatsprocket 24 cannot operate to mutilate or destroy sprocket holes in thefilm, the film rides loosely between pinch roll 140 and the puck tire.On the other hand, as soon as the tension in the film between idlerroller 138 and sprocket 24 exceeds the desired level, drive arm 135 isdisplaced clockwise about pivot 136, against the bias of spring 142, todisplace the film at the pinch roll into contact with puck tire 131.Puck shaft 132 is continuously rotated in a clockwise direction duringforward mode operation of the projection station at a rate which is soselected relative to the effective diameter of the puck that theperipheral surface of puck tire 131 has a velocity greater than theperipheral velocity of sprocket 24. Therefore, as soon as mechanism 121senses that film 7 passing through the mechanism has a tension levelgreater than the predetermined tension level associated with thestiffness of spring 142, the mechanism responds to such increasedtension to move the film into contact with the puck tire to overdrivethe film through mechanism 121 relative to sprocket 24. Such overdrivingaction of the puck produces an immediate reduction in the tension offilm approaching sprocket 24.

Referring to accompanying FIGS. 2 and 5. Puck shaft 132 extends from therear face of bearing block 134 through an oversized opening 148 in frameplate to a pulley assembly 149. Pulley assembly 149 includes a hub 150which is mounted to the rear end of shaft 132 by an overruning clutch151. The exterior of hub 150 carries a timing belt pulley 152. Hub 150is held in a desired position axially of puck shaft 132 by suitablemeans which preferably includes a spacer sleeve 153 disposed about theshaft within aperture 148. Clutch 151 is disposed between shaft 132 andhub 150 so that clockwise rotation of the hub (when viewed from the leftin FIG. 2) is transferred by the clutch to shaft 132. Counterclockwiserotation of the hub relative to the shaft is accommodated and permitedby clutch 151. A timing belt 154 is engaged between pulley 152 and asmall diameter pulley 155 secured to lower sprocket drive shaft 47adjacent gear 125. it is apparent, therefore, that the clockwiserotation of puck 130 is synchronized to the rotation of upper shuttleloop sprocket 24; by virtue of the relative diameters of pulleys 155,152 and puck 130, the puck has a peripheral speed when rotated clockwisewhich is a selected amount greater than the peripheral speed of uppersprocket 24 when the latter is rotated counterclockwise, as in the caseduring forward mode operation of projection station 120.

During reverse mode operation of projection station 120, as in therewinding of film from the takeup reel to the supply reel as whereprojection station is a component of a projection system of the typedescribed in US. Pat. No. 3,617,117, for example, the principal locus ofthe problem of excess film tension is shifted from adjacent uppersprocket 24 to adjacent lower sprocket 74. Accordingly, lower filmtension control mechanism 122 is provided along the path of film 7nextadjacent lower sprocket 74 in a direction along the film path fromthe sprocket toward the takeup reel. Mechanism 122 is provided forregulating the tension in film approaching the lower sprocket tomaintain the film tension within acceptable levels below the thresholdof sprocket hole mutilation or destruction by sprocket 74.

As shown in accompanying FIGS. 1 and 3, lower film tension controlmechanism 122 includes a puck wheel 157, the exterior surfaces of whichare defined by a rubber tire 158, carried by a shaft 159 rotatablymounted in a bearing block 160 by suitable bearings (not shown, butsimilar to bearings 134 for upper puck shaft 132). A drive arm 161 ispivoted at 162 to bearing block 160 at a location substantially directlybelow puck shaft 159. As shown in accompanying FIG. 1, drive arm 161 isof substantially L-shaped configuration when viewed in elevation, andcarries a pinch roll 163 rotatable about an axis 164. Pinch roll axis164 is disposed adjacent the intersection of the horizontal and verticallegs of the L-shaped drive arm, whereas pivot axis 162 for the drive armrelative to bearing block 160 is defined adjacent the end of thehorizontal shorter leg of the drive arm. An idler roller 165 isrotatably mounted to the upper end of the vertical leg of the drive armadjacent the guide roll 178 (shown but not numbered in US. Pat. No.3,201,020) around which film 7 is led from the interface between lowershuttle loop sprocket 74 and lower guide shoe 76. Another idler roller166 is rotatably mounted on a support lug 167 which extends to the rightfrom bearing block 160 so that idler roller 166 is disposed immediatelyadjacent lower puck 157.

The path of film 7 from sprocket 74 is around idler roller 165 in such amanner that tension in the film induces drive arm 161 to rotateclockwise about pivot 162. From roller 165, the film path is around theportion of idler roller 166 opposite (not adjacent) puck 157, thenbetween the puck and pinch roll 163 and onward toward the takeup reel.This threading of film 7 through control mechanism 122 is such that whendrive arm 161 rotates clockwise about pivot 162, pinch roll 163 movestoward puck 157 and tends to urge the film between it and the puck intointimate engagement with the tire carried by the puck. A spring 168 iscoupled between bearing block 160 and drive arm 161 for biasing thedrive arm to rotate counterclockwise about its pivot 162. The stiffnessof spring 168 is selected so that when the tension in film 7 adjacentsprocket 74 exceeds that tension level which has been determined toconstitute the threshold of sprocket hole mutilation or destruction bythe sprocket, drive arm 161, in response to film tension sensed by itvia idler roller 165, rotates clockwise about pivot 162 sufficiently tocause pinch roll 163 to force the adjacent film into contact with puck157.

During reverse mode operation of projection station 120, shaft 159 isrotated counterclockwise at a rate such that the peripheral speed ofpuck 157 exceeds, by

a selected amount, the peripheral speed of lower shuttle loop sprocket74. Therefore, if the tension in film 7 immediately adjacentsprocket 74exceeds the mutilation threshold tension level, this fact is sensed bymechanism 122 and the film is operatively engaged in drivingrelationship with puck 157 so that the puck functions to overdrive thefilm relative to sprocket 74. Overdriving of the film adjacent thesprocket relative to the sprocket results in thefilm tending to go slackadjacent the sprocket. It is apparent, therefore, that control mechanism122 functions, during reverse mode operation of projection station 120,to maintain film 7 adjacent lower shuttle loop sprocket 74 at tensionlevels which are below the sprocket hole mutilation threshold tensionlevel. Sprocket 74 is able to operate on low tension film throughoutreverse mode operation of the projection station without the likelihoodthat the lower sprocket will mutilate film 7 or lose a frame relative tothe predetermined length of film in shuttle loop 123.

The drive of lower puck 157 is illustrated in accompanying FIGS. 3 and5. Puck shaft 159 extends rearwardly from bearing block 160 through anoversized aperture 169 formed in frame plate 2 to a pulley assembly 170.The pulley assembly includes a hub 171 which is mounted to the rear endof shaft 159 by an overrunning clutch 172. The clutch is so disposedbetween the hub and shaft 159 that the hub is not permitted to rotatecounterclockwise relative to the shaft (viewing the shaft end-on fromthe right in FIG. 3), but clockwise rotation of the hub relative to theshaft is accommodated and permitted by the clutch. A timing belt pulley173 is carried by hub 171 coaxially of the shaft adjacent the rear offrame plate 2. The pulley assembly is held in the desired positionaxially of shaft 159 by suitable means which preferably include a spacersleeve 174 disposed about the shaft between bearing block 160 and thepulley assembly. A timing belt 175 is engaged between pulley 173 and alarge diameter pulley 176 which is affixed to the rear end of lowersprocket shaft 47 between pulley 155 and gear 125. It is apparent,therefore, that during reverse mode operation of the projector station120, puck 157 is driven counterclockwise at a rate such that theperiphery of the puck has a velocity which is a selected amount greaterthan the peripheral velocity of lower shuttle loop sprocket 74.

Film tension control mechanisms 121 and 122 are therefore seen tofunction during both forward and reverse mode operation of projectionstation 120 to supply film at low tension levels to that one ofsprockets 24 or 74 which operates to supply film to shuttle loop 123.Accordingly, the input sprocket to the shuttle loop is not required topull against film at high tension levels, with the result that thetendency for the sprocket to mutilate the sprocket holes formed in thefilm is eliminated. Also, the likelihood that the supply sprocket willpass less than 24 frames of film for any given second of operation ofthe projection station is greatly reduced.

Another film tension control mechanism 180 is illustrated inaccompanying FIG. 4 and may be used if desired in place of film tensioncontrol mechanism 121, particularly in cases where the film adjacentupper shuttle loop sprocket 24 outside of shuttle loop 123 is likely tobe subjected to unduly high tension levels during both forward andreverse modes of operation of projector station 120. Mechanism 180 issubstantially identical to control mechanism 121 except in the manner bywhich puck shaft 132 is driven by timing belt 154. The drive arrangementfor puck shaft 132 in control mechanism 180 includes a pulley assembly181 which includes a hub 182. Timing belt pulley 152 is carried by theexterior of hub 182. The hub is mounted on the rear end of puck shaft132 by an overrunning clutch 183 and a journal bearing 184. Clutch 183is arranged to prevent hub 182 from rotating clockwise relative to shaft132 (viewing the shaft end-on from the left in FIG. 4), but toaccommodate and permit counterclockwise rotation of the hub relative tothe shaft. A pinion gear 185 is carried by hub 182 adjacent timing beltpulley 152 at the end of the hub opposite from frame plate 2. Gear 185meshes with a large diameter idler gear 186 secured to a gear hub 187mounted by a journal bearing 188 to the rear end of an idler gear shaft189. The idler gear shaft passes through an oversize opening 190 inframe plate 2 to bearing block 133 where the idler gear shaft issupported. A small diameter idler gear 191 is also carried by idler gearhub 187 and meshes with a drive gear 192. Drive gear 192 has a greatereffective diameter than pinion gear 185 and is mounted to puck shaft 132by an overrunning clutch 193. Clutch 193 is mounted to the shaft in thesame sense as clutch 183, i.e., clutch 193 prevents gear 192 fromrotating clockwise relative to shaft 132 but accommodates and permitscounterclockwise rotation of its gear relative to the puck shaft.

During forward mode operation of film tension control mechanism 180,puck is rotated clockwise when viewed as in FIG. 1 at a rate determinedby the angular velocity of timing belt pulley 152. During such forwardmode operation, gear 192 is driven via idler gears 186 and 191 frompinion gear 185 with an angular velocity which is less than that oftiming belt pulley 152. Accordingly, during forward mode operation ofmechanism 180, drive gear 192 tends to rotate counterclockwise relativeto shaft 132 and this manner of rotation of the gear is the type ofrotation accommodated and permitted by clutch 193. Therefore, duringforward mode operation, control mechanism 180 functions in exactly thesame way as control mechanism 121 to regulate and control the tension atwhich film is supplied to upper shuttle loop sprocket 24.

During reverse mode operation of projector station 120, timing beltpulley 152 is driven by belt 154 counterclockwise relative to shaft 132,and the gear ratio between pulley 152 and drive gear 192 is such thatgear 192 is driven counterclockwise about the axis of shaft 132 but at arate less than that of timing belt pulley 152. Clutches 183 and 193accommodate these counterclockwise rotations about shaft 132 such thattiming belt 154 is ineffective to drive shaft 132 counterclockwise.

During reverse mode operation of the projector station, idler roller 138functions in the manner described above to sense the tension in film 7being fed from upper shuttle loop sprocket 24 toward the controlmechanism as this sprocket operates to extract film from shuttle loop123. If idler roller 138 senses that the tension in film 7 between itand sprocket 24 is too great, i.e., the rate of film movement throughcontrol mechanism 180 is too great, drive arm rotates clockwise aboutits pivot axis 141 so that the film between pinch roll and puck 130 isforcefully driven by the pinch roll into frictional engagement with thepuck tire. When this occurs, the film itself tends to drive puck 130counterclockwise, and such counterclockwise rotation of the puck can beaccommodated so long as shaft 132 is not driven counterclockwise at arate greater than the counterclockwise rotation of drive gear 192 aboutthe shaft axis. Counterclockwise rotation of shaft 132 at a rate greaterthan counterclockwise rotation of drive gear 192 about the shaft axisresults in the gear appearing to rotate clockwise about the shaft.Clutch 193, however, prevents gear 192 from rotating clockwise aboutshaft 132.- Accordingly, the maximum angular velocity of shaft 132counterclockwise about its axis is defined by the rate at which drivegear 192 is driven counterclockwise about the shaft axis via the gearsbetween it and timing belt pulley 152. The overall gear ratio defined bythe train of gears 185, 186, 191 and 192 is selected so that the maximumcounterclockwise angular velocity afforded to puck 130 is slightly lessthan the angular velocity of upper shuttle loop sprocket 24 duringreverse mode operation of the projection station. It is seen, therefore,that when idler roller 138 senses an excess tension level in film 7between it and sprocket 24, control mechanism 180 operates to move thefilm between pinch roll 140 and the puck into frictional engagement withthe puck so that the puck operates as a brake or retardant to the motionof film past it. Puck 130, therefore, underdrives film 7 relative tosprocket 24 when mechanism 180 senses that the film adjacent thesprocket is subject to tension in excess of the mutilation thresholdtension level. Underdriving of film 7 by film control mechanism 180induces the film to go slack between it and sprocket 24. In this manner,control mechanism 180 operates to maintain tension in film 7 adjacentsprocket 24 at tension levels below the mutilation threshold tensionlevel during reverse mode operation of projector station 120.

It will be appreciated that the drive for lower puck 157 may be modifiedin the same manner as mechanisms 121 and 180 differ from each other,thereby to impart an overdrive/underclrive operating characteristic tothe lower film tension control mechanism.

Film tension control mechanisms 121, 122 and 180 described above may beused to advantage in any motion picture projector in which thelikelihood exists that film will be subjected to undue tension levelsadjacent the shuttle loop sprockets during forward or reverse modeoperation of the projector. These mechanisms are particularly useful inprojectors where the film supply and takeup reels are of increasedcapacity and therefore possess unusually high inertia. It is apparent,therefore, that film control mechanisms 121, 122 and 180 may be used toadvantage in a projection system like that described in U.S. Pat.3,6l7,ll7, notwithstanding the fact that the supply and takeup reels insuch a system preferably are equipped with tension responsive drivemechanisms like those shown in U.S. Pat. 3,398,914, for example. The useof film tension control mechanisms 121, 122 and 180 is not dependentupon the incorporation in the projector station of apparatus accordingto reference U.S. Pat. 3,201,020.

As noted above, U.S. Pat. 3,6l7,l 17 describes a projection system inwhich the rewinding operation is performed via the projection station.That is, during rewinding of film, the film moves along the same path asis defined through the projection system for display of the informationcarried by a given length of film. The pull-down mechanism used to movefilm on a frame-byframe basis through shuttle loop 123 must be operatedduring the use of the projectors of the system according to U.S. Pat.No. 3,6l7,1 17. The operation of the frameby-frame film advancemechanism during reverse mode of such projectors, however, is a sourceof potential damage to the film, particularly where a frame is lost fromthe shuttle loop past either the upper shuttle loop sprocket or thelower shuttle loop sprocket during reverse mode operation. Duringforward mode operation,

the film in a conventional shuttle loop is slack adjacent both of thesprockets defining the ends of the shuttle loop. Projection station 120,however, includes a mechanism 200 for maintaining the film in shuttleloop 123 under moderate acceptable levels of tension, at least adjacentthe upper shuttle loop sprocket and preferably adjacent both sprockets,during reverse mode operation of the projector station. The maintenanceof the shuttle loop film under moderate tension levels during reversemode operation of the projector station assures that excess tensionlevels in the film outside the shuttle loop will be minimally effectiveto cause the shuttle loop sprockets to lose a frame relative to thepredetermined length of film required to define a proper shuttle loop.

The projection station shown in accompanying FIG. 1 preferably uses aSeries 500 Bell & Howell motion picture projector equipped with anAUTOLOAD selfthreading mechanism (such as per referenced U.S. Pat.3,201,020), but modified in the manner shown to accommodate film tensioncontrol mechanisms 121 and 122, for example, and also to accomodatemechanism 200, which is referred to herein as a tight-loop rewindmechanism.

Tight-loop rewind mechanism 200 includes a solenoid 201 having areciprocal armature 202. The solenoid is mounted to the front ofprojector housing 12 above the upper end of shuttle loop 123 so that thearmature 202 is disposed above upper shuttle loop sprocket 24. The outerend of the armature is disposed above and spaced from pivot axis 32 ofthe selfthreading mechanism shown in FIGS. 2 and 3 of referenced U.S.Pat. No. 3,201,020, for example. A link 203 is pivoted at 204 to theouter end of the solenoid armature. Link 203 is also securely clamped topivot shaft 32 so that the pivot shaft is rotated in response tooperation of solenoid 201. As shown best in accompanying FIG. 6, one endof a link 33 is fixed to shaft 32 within housing 12 and cooperates witha link 205 (a part of the structure described in U.S. Pat. No. 3,201,020but not numbered therein) affixed to pivot shaft 22 within the housingadjacent the drive gear for upper sprocket 24. Links 33 and 205 are sointerconnected that clockwise rotation of pivot shaft 32 producescounterclockwise rotation of pivot shaft 22, and vice versa. The forwardend of pivot shaft 22 is disposed between upper shuttle loop sprocketshaft 25 and guide roll 28 behind upper shuttle loop sprocket 24; guideroll 28 defines the upper end of shuttle loop 123. One end of a lever206 is secured to the forward end of pivot shaft 22 and has its otherend pivoted at 67 to the upper end of the vertically disposed,reciprocable connecting link 64. Lever 206, upon comparison ofaccompanying FIG. 1 with FIG. 2 of referenced U.S. Pat. No. 3,20l ,020,will be seen to be a modification of lever 21 illustrated and describedin the referenced patent. A bracket 207 is affixed to link 64 closelyadjacent pivot 67 and mounts a rotatable idler roller 208.

An idler roller 92 is located adjacent the path of the film definingshuttle loop 123 near lower shuttle loop sprocket 47. Idler roller 92 isa component of the shuttle loop restoring mechanism described inreferenced US. Pat. No. 3,201,020 and illustrated particularly in FIGS.9 and 10 thereof. Idler roller 92 is disposed near the lower end of link64 which is pivoted at 45 to a lever 48 which is mounted for rotationabout shaft 47 for the lower sprocket. Pivot 45 is also associated withone end of a link 63 the other end of which is interconnected by pivot57 to a lever 55 which has a projection 58 disposed above the supportshaft for idler roller 92.

Tight-loop rewind mechanism 200 is illustrated in accompanying FIG. 1 inits actuated condition, which is the condition of the mechanism duringreverse mode operation of projection station 120 for rewinding of film7. In the actuated condition of mechanism 200, solenoid 201 is energizedto retract armature 202, thereby to rotate pivot shaft 32counterclockwise against the bias of a spring 226 (see accompanying FIG.6) which is engaged between link 33 and housing 12. Such retraction ofsolenoid armature 202 produces clockwise rotation fof pivot shaft 22which, via lever 206, reciprocates link 64 upwardly so that idler roller208 has the position illustrated in solid lines in accompanying FIG. 1.Such upward motion of link 64 produces downward movement of idler roller92 to the position shown in solid lines in accompanying FIG. 1. Thismotion of idler roller 92 in response to upward movement of link 64results from the interconnection of link 64 and roller 92 via link 63,pivot pin 57, lever 55 and projection 58. Upward movement of idlerroller 208 and downward movement of idler roller 92 brings these rollersinto engagement with the portion of film 7 which defines shuttle loop123 and pulls the film taut over these rollers. Upward movement of lever64 also causes cam 90 of bracket 91 to engage the end 89a of pin 89 todisable the frame-by-frame film advance mechanism, thereby preventingteeth 88 of shuttle 87 from engaging in the sprocket holes defined byfilm 7. Also, upward movement of link 64 causes projection 114 to engagecam bracket 115 and move pressure plate 39 out of contact with the filmengaged between side guides 36 in gate assembly 34.

Solenoid 201 is wired so that it energizes when the control circuit forprojection station 120 is operated to place the projection station inits reverse mode wherein lower shuttle loop sprocket 74 rotatescounterclockwise to feed film into the shuttle loop, and upper shuttleloop sprocket 24 rotates clockwise to extract film from the shuttleloop. During such operation of the projector station, the frame-by-frameadvance mechanism of the projector is disengaged and the film betweenidler rollers 92 and 208 moves freely through the gate assembly betweenpressure plate 39 and rear plate 35. On the other hand, when the controlcircuitry for projection station 120 is disposed to operate theprojection station in its forward mode, solenoid 201 is not energizedand spring 68 is effective upon link 33 to rotate pivot shaft 32clockwise and to move link 64 downwardly. Downward movement of link 64causes roller 208 to be moved into the position shown in broken lines inaccompanying FIG. 1. Also, downward movement of link 64 results in loweridler roller 92 being moved to the position shown in broken lines inaccompanying FIG. I; this occurs by virtue of the above-describedinterconnection between link 64 and roller 92 via pivot 45, link 63,pivot pin 57, lever 55 and projection 58. When idler roller 92 is in theposition shown in broken lines in accompanying FIG. 1, idler roller 92functions as a component of the shuttle loop restoration mechanism.Also, downward movement of link 64 causes cam to move clear of the end89a of pin 89 whereby the frameby-frame advance mechanism is placed intoits opera tive condition; such movement also frees projection 114 fromengagement with cam bracket 115 whereby pressure plate 39 is enabled tofunction in its desired manner. The movement of idler rollers 92 and 208into the positions shown in broken lines in accompanying FIG. 1 placesthese rollers clear of the film defining shuttle loop 123. Thus, theframe-by-frame advance mechanism may operate in its intendeddiscontinuous manner simultaneously with continuous operation of shuttleloop sprockets 24 and 74 to feed film to the shuttle loop and to extractfilm from the shuttle loop, respectively.

In view of the foregoing, it is apparent that when projection station isoperated in its reverse mode for the rewinding of film 7, mechanism 200operates to engage the film within the shuttle loop. The structure ofmechanism 200 is arranged so that when the shuttle loop film is engagedby roller 208, the film is under tension at levels below the mutilationthreshold tension level. The tension of the film in the shuttle loopcounteracts and tends to offset the tension in film outside the filmloop, but adjacent to sprockets 24 and 74. It is apparent, therefore,that mechanism 200 is itself operative during reverse mode operation ofprojection station 120 to greatly reduce the tendency for either ofsprockets 24 or 74 to lose a frame relative to film 7, and is alsoeffective to produce significant control over the tension levels presentin film 7 at and adjacent the shuttle loop sprockets. As a result, thepresence of mechanism 200 means that there is a greatly reducedlikelihood that sprockets 24 or 74 will operate during reverse modeoperation of the projection station to mutilate destroy the sprocketholes defined in film 7; this benefit is provided by tight-loop rewindmechanism 200 itself and is not dependent upon the presence in theprojection station of film tension control mechanisms 121 and 122, forexample. It is preferred, however, that a tight-loop rewind mechanismand the film tension control mechanisms be provided in combinationwithin projection station 120 to reduce to the greatest extent possiblethe tendency of the film to malfunction at sprockets 24 or 74 or at theframe-by-frame advance mechanism, during either forward or reverse modesof the projection station.

It is preferred that solenoid 201 be connected to the control circuitryfor projection station 120 so that the solenoid is energized during bothreverse and standby modes of operation of the projector station. Thestandby mode of projector station 120 is a mode in which power issupplied to the projector station but drive motor 127 is not operated.The standby mode of the projection station may be used to advantageduring the threading of film along the path illustrated in accompanyingFIG. 1, for example.

Another tight-loop rewind mechanism 210 is illustrated in accompanyingFIGS. 7 and 8 and differs from tight-loop rewind mechanism 200 only inthe manner in which lever 206 is indexed to produce reciprocation ofconnecting link 64. Tight-loop rewind mechanism 210 does not includesolenoid 201 or link 203, but it does include pivot shaft 32, link 33,link 205, pivot shaft 22 and spring 226 biased between projector housing12 and link 32 in association with pivot shaft 32; spring 226 issubstituted for spring 68 shown in U.S. Pat. No. 3,201,020. As shown inaccompanying FIGS. 7 and 8, upper shuttle loop sprocket 24 includes adrum 211. The rear portion of the drum defines a cavity 212 which openstoward the front face of projector housing 12 concentric to the driveshaft 25 for the upper shuttle loop sprocket. Drum 211 is secured toshaft 25 by appropriate means (not illustrated) for rotation with theshaft. A sleeve 213 is connected to the drum and extends about shaft 25to an externally threaded rear end disposed in substantial abutment withthe front face of housing 12 coaxially of cavity 212. An axially boredbearing 214 for an actuating lever 215 is rotatably mounted about sleeve213 around the unthreaded portion of the sleeve. The bearing has acircumferential flange 216 which, as shown best in accompanying FIG. 7,is preferably hexagonally configured when the bearing is viewed end-on.Flange 216 cooperates within a correspondingly configured opening 217formed in an end of actuating lever 215 so that the actuating lever andbearing 214 are keyed together for rotation as a unit about shaft 25.Bearing flange 216 and the adjacent end of actuating lever 215 aredisposed between a pair of friction disks 218. One of the friction diskshas one of its faces abutted against the portion of drum 211 definingthe base of cavity 212 and has its other face abutted against theadjacent faces of bearing flange 216 and actuating lever 215. The otherfriction disk has one of its faces abutted against the opposite surfacesof the bearing flange and the actuating lever, and its other facebearing against an annular pressure plate 219 disposed concentricallyabout sleeve 213 and keyed to the sleeve. An annular spring washer 220is interposed between pressure plate 219 and a nut 221 engaged upon theexternally threaded end of sleeve 213. Preferably friction disks 218 aredefined by cork or some other material which manifests a highcoefficient of friction against the metal used to define drum 211,bearing 214, actuating lever 215 and pressure plate 219.

As illustrated in accompanying FIG. 7, actuating lever 215 has anactuating end 222 in which is formed an elongated opening 223 throughwhich pivot pin 67 is passed. Pivot pin 67 is affixed to the upper endof connecting link 64 and is snugly journalled within the adjacent endof lever 206. Accordingly, a rotatable connection is provided by pivotpin 67 between lever 206 and connecting link 64, whereas a slidable androtatable connection is provided between actuating lever 215 andconnecting link 64 via elongated slot 223.

Nut 221 is tightened against spring washer 220 sufficiently' thatbearing flange 216 and the inner end of actuating lever 215 are snuglyclamped between friction disks 218. The frictional engagement of thefriction disks with actuating lever 215 circumferentially of shaft 25 issufficient that, when shaft 25 is rotated counterclockwise, as duringforward mode operation of sprockets 24 to feed film 7 to shuttle loop123, the torque imposed upon actuating lever 215 by the friction disksis sufficient to overcome the bias of spring 226 (a balance springprovided so that the friction clutch assembly works againstsubstantially the same load for either direction of rotation of sprocket24) as manifested at pivot pin 67 via links 33 and 205, shaft 22 andlever 206. Accordingly, during forward mode operation of a projector inwhich tight-loop rewind mechanism 210 is incorporated, idler rollers 208and 92 are held in their retracted positions represented in broken linesin accompanying FIG. 1. During reverse mode operation of the projector,upper shuttle loop sprocket 24 rotates clockwise to extract film fromshuttle loop 123. As the upper sprocket rotates clockwise, such rotationis effective via friction disks 218 to impart to actuating lever 215 atorque acting clockwise about shaft 25. Accordingly, as upper sprocket24 begins to rotate clockwise, actuating lever 215 is indexed clockwiseabout shaft 25 with the bias of spring 226, thereby to move connectinglink 64 upwardly so that idler roller 208 moves into film guiding andtautening engagement with the film in the upper portion of shuttle loop123. As is apparent from the preceding description, upward movement ofconnecting link 64 produces downward movement of idler roller 92 intofilm guiding and tautening engagement with the film in the lowerportions of the shuttle loop. Also, upward movement of the connectinglink disengages the frame-byframe film advance mechanism and disengagespressure plate 39 from engagement with the film in the vicinity of gateassembly 34. The benefits accruing from engagement of film in theshuttle loop by idler rollers 208 and 92 during reverse mode operationof the projector have been set forth above. The limit of upward movementof connecting link 64 is defined by the elongate extent of opening 223formed in the operating end of actuating lever 215; in tight-loop rewindmechanism 200, this limit is defined by the throw of solenoid arm ature202.

It is apparent, therefore, that tight-loop rewind mechanism 210 isresponsive to reverse mode operation of a projector in which themechanism is incorporated to disable the frame-by-frame film advancingmechanism from effective advancing cooperation with the film, and alsoto define a part of the film path (corresponding to the shuttle loop)which is of definite configuration and fixed length within which thefilm is held taut at moderate levels of tension well below themutilation threshold tension level for the film. It is noted, however,that tight-loop rewind mechanism 210 may not be placed automaticallyinto its operated position during standby mode operation of theprojector from its show mode since, during standby mode operation, uppersprocket 24 is not rotating. counterclockwise movement of the actuatinglever about shaft 25 corresponds to operation of mechanism 210 into itsunoperated state. Because mechanism 210 is in it unoperated state whenthe projector is placed in its standby mode, tightloop rewind mechanism200 constitutes the presently preferred tight-loop rewind mechanismaccording to this invention.

It will be apparent from the foregoing description that both tight-loopmechanisms 200 and 210 incorporate many of the same structural elements,features and operations as are provided in a self-threading mechanism ofthe type described in referenced U.S. Pat. No. 3,201,020. It is for thisreason that it is presently preferred that a tight-loop rewind mechanismaccording to this invention be provided in the context of a motionpicture projector originally designed and constructed for inclusion ofthe self-threading apparatus of U.S. Pat. No. 3,201,020.

It is noted that the provision of the tight-loop rewind mechanismaccording to this invention does not impair the function of idler roller92 as a component of a shuttle loop restoring mechanism during forwardmode operation of the projector.

It will be apparent that film tension control mechanisms 121, 122 and180, on the one hand, and tightloop rewind mechanisms 200 and 210, onthe other hand, are all addressed to the same basic objective, namely,greatly reducing if not altogether eliminating the likelihood that theprojector mechanism will act upon damaged or improperly conditioned filmat any time during its operation to produce mutilation of the sprocketholes defined in film 7. It is for this reason that it is preferred"that a suitable film tension mechanism be used in conjunction with asuitable tight-loop rewind mechanism, although joint use of a filmtension control mechanism with the tight-loop rewind mechanism is notessential to the realization of the benefits afforded by theimprovements described above.

Tight-loop rewind mechanism 200 may be placed into its operatedcondition by putting the projector in its standby mode. Also, mechanism210 may be actuated manually into its operated position when theprojector is either off or in -a standby mode. Tight-loop rewindmechanisms 200 and 210, when disposed in their operated conditions,-substantially exactly define the path along which film 7 should bethreaded through the shuttle loop for proper operation of the projector.Mechanisms 200 and 210 are so arranged that film may be threadedmanually through the projector. The automatic film threading apparatusdescribed in US. Pat. No. 3,201,020, however, is so arranged to preventmanual threading of 'fi lm through the projector. Mechanisms 200 'or210, therefore, may be used to advantage in motion picture projectorsintended for home and non-commercial use to precisely define the desiredpath for manual threading of film; such projectors would eliminate alldiscretion by the operator concerning how to thread film through theshuttle loop, thereby eliminating another significant cause of film jumpor chatter.

The film and control mechanism 121 described above can be used not onlyto control tension but to provide buffering between the supply reel andthe intermittent drive of the film through the operational zone in whichthe optical system is located. Such an arrangement is shown in themodification of FIG. Referring to FIG. 9, it will be seen that the film7 passes through the tensioning mechanism 121, extending around theidler 138 andpassing directly to the roller 208. Thus the sprocket drive24 and associated guides 27 and 28 provided in "the arrangement of FIG.1 are eliminated.

In this simplified arrangement, the film between the idlers 138 and 208is slack since the puck 130, when engaged by the film, tends to feed thefilm toward the inner lip mechanism at a slightly faster rate than it ismoved through the operational zone. However, this slack in the filmallows the idler arm 138 and associated arm 135 to be urged by thespring 142 so as to move the pinch roller 140 away from the puck 130.the film 7 is then released from engagement with the puck 130,interrupting the movement of the film 7 toward the operational zone. Asthe intermittent drive mechanism moves film through the operationalzone, the slack in the film between the idlers 138 and 208 is taken up,and the tension increases, causing the idler 138 to again move the arm135 and the pinch roller 140 towards the puck 130. The action of thepuck causes additional film to be pulled off the supply reel,reestablishing the slack in the film between the idlers 138 and 208. Inthis way, the tensioning mechanism 121 provides a buffer between thesupply reel and the intermittent drive mechanism, so that theintermittent drive mechanism does not have the full load of withdrawingthe film from the supply reel. The film tensioning mechanism 121 thusprevents any tearing of the film at the sprocket holes which otherwisemight be caused by the intermittent drive mechanism if the full load ofwithdrawing film from the supply reel were transferred through tensionin the film directly to the intermittent drive mechanism.

In the reverse mode, when the film is being rewound back on the supplyreel and tension is being applied to the film, excess tension can tearthe sprocket holes on the teeth of the lower sprocket 74. The lowerspeed of the puck 130 then acts as a brake because its rotational speedis limited to a surface speed less than the linear speed of the film, inthe manner described above in connection with FIG. 4.

From the above description, it will also be appreciated that thetensioning mechanism 121 could be used for buffering the transfer offilm or magnetic tape from the supply reel to the operational zone infilm transport mechanisms in which the film is moved at a continuousrate through the operational zone. Thus while not specifically shown, itwill be understood that the tensioning mechanism arrangement is notlimited to use only with perforated film and an intermittent sprocketdrive mechanism.

Workers skilled in the art to which this invention pertains will readilyrecognize that the film tension control mechanisms and tight-loop rewindmechanisms described above may be modified or altered without departingfrom the scope of this invention. The specific structural arrangementsillustrated in the accompanying drawings and described above have beenpresented for the purposes of example and because they constitutepresently preferred embodiments of this invention. The foregoingdescription should not be construed as limiting the scope of thisinvention.

What is claimed is:

1. Apparatus 'for feeding strip material in either direction through anoperational zone between two storage regions comprising reversible drivemeans engagable with the strip material for moving the strip through theoperational zone in either direction, and tension control meanspositioned along the path of the strip between the supply source and thedrive means, the tension control means including reversible'drive meansengagable with the strip material for driving the strip material at aspeed greater than the average speed at which the strip is moved throughthe operational zone in one direction and driving the strip material ata speed less than said average speed in the other direction, and meansresponsive to variations in the tension in the strip between one of saidstorage regions and the first drive means for activating the seconddrive means when tension in the strip exceeds a predetermined level andfor inactivating the second drive means when the tension in the stripdrops below a predetermined level.

2. Apparatus as defined in claim 1 wherein the second drive meansincludes a rotating member adjacent the path of the strip, and saidmeans activating the second drive means includes a pinch roller, thestrip passing between the pinch roller and the rotating member, andmovable means engaging the strip and movably supporting the pinchroller, said movable means responding to variations in the tension ofthe strip for moving the pinch roller into and out of engagement withthe rotating member.

3. Apparatus according to claim 2 wherein the means for moving the pinchroller includes a pivotable lever to which the pinch roller is mounted,and a guide roller rotatably mounted to the lever in spaced relation tothe pinch roller and the lever pivot axis and defining a bend in thestrip material.

4. Apparatus according to claim 3 wherein the pinch roller is mounted tothe lever between the guide roller and the lever pivot axissubstantially closer to the pivot axis than to the guide roller.

5. Apparatus according to claim 3 including means biasing the leverabout its pivot axis in a direction productive of movement of the pinchroller away from the rotating member, the bias of said means beingselected to define the tension level in the strip material.

6. Apparatus as defined in claim 2 wherein the second drive meansfurther includes a rotatable shaft to which the rotating member ismounted, a drive pulley disposed concentric to the drive shaft, andoverrunning clutch means disposed between the drive pulley and the shaftfor coupling the pulley in driving relation to the shaft when the pulleyis driven in a direction corresponding to movement of the strip towardthe operational zone.

7. Apparatus according to claim 6 including a gear disposed concentricto the drive shaft, second overrunning clutch means disposed between thegear and the drive shaft for coupling the gear in driving relation tothe shaft when the gear is rotated in a direction corresponding tomovement of the strip toward the operational zone, and gear meanscoupled between the drive pulley and the gear for rotating the gearabout the shaft axis at a rate less than the rate of rotation of thedrive pulley about the shaft axis.

8. Apparatus' as defined in claim 2 wherein the second drive meansincludes a rotatable drive shaft to which the rotating member ismounted, means including a first overrunning clutch coupled to the driveshaft for driving the shaft in one direction at said greater speed, andmeans including a second overrunning clutch for limiting rotationalspeed of the shaft in the opposite direction to said lesser speed.

9. In a motion picture projector having a film supply reel, an uppershuttle loo'p sprocket, a gate assembly which includes a frame-by-framefilm advance mechanism, a lower shuttle loop sprocket and a film takeupreel disposed in serial order along a film path which traverses anoptical axis of the projector with a shuttle loop defined between thesprockets, and reversible drive means connected to the reels andsprockets for moving the film in either direction between the reels, theimprovement comprising film tension control means disposed nextadjacentone of the sprockets along the film path toward the adjacent reel, saidfilm tension control means including first means operative in responseto a film tension level in excess of a predetermined tension level inthe adjacent film for driving the film along the path toward the onesprocket at a rate greater than the rate of film advance by the onesprocket in one direction, and second means operative in response to afilm tension level in excess of a predetermined tension level in theadjacent film for braking the film along the path toward the one reel toa rate below the rate of film advance by the one sprocket in the reversedirection.

10. Apparatus according to claim 9 wherein the film tension controlmeans includes a rotatable film drive puck disposed proximate the filmpath so as to be spaced from film moving along the path when adjacentfilm has a tension level less than said predetermined tension level, apinch roller disposed proximate the other side of the film path adjacentthe puck, and means responsive to a film tension level in excess of saidpredetermined tension level for moving the pinch roller toward the pucksufficiently to cause film moving along the path to engage the puck.

11. Apparatus according to claim 10 wherein the means for moving thepinch roller includes a pivotable lever to which the pinch roller ismounted, and a film guide roller rotatably mounted to the lever inspaced relation to the pinch roller and the lever pivot axis anddefining a bend in the film path.

12. Apparatus according to claim 11 wherein the pinch roller is mountedto the lever between the guide roller and the lever pivot axissubstantially closer to the pivot axis than to the guide roller.

13. Apparatus according to claim 11 including means biasing the leverabout its pivot axis in a direction productive of movement of the pinchroller away from the puck, the bias of said means being selected todefine said predetermined film tension level.

14. Apparatus according to claim 11 wherein the film guide roller isdisposed nextadjacent the pinch roller along the film path between thepinch roller and the adjacent shuttle loop sprocket.

15. Apparatus according to claim 11 including an idler roller disposedalong the film path at a fixed location between the film guide rollerand the pinch roller, the film guide roller being located effectivelynextadjacent the adjacent shuttle loop sprocket along the film path.

16. Apparatus according to claim 10 wherein the first means operative inresponse to film tension includes means for driving the puck with aperipheral velocity of selected amount greater than the peripheralvelocity of the adjacent sprocket and in a direction corresponding tomovement of film adjacent the puck toward the adjacent sprocket when theadjacent sprocket is driven to supply film to the shuttle loop.

17. Apparatus according to claim 16 wherein the puck drive meansincludes a rotatable drive shaft to which the puck is mounted, a drivepulley disposed concentric to the drive shaft, and overrunning clutchmeans disposed between the drive pulley and the shaft for coupling thepulley in driving relation to the shaft when the pulley is driven in adirection corresponding to movement of film adjacent the puck toward theone sprocket.

18. Apparatus according to claim 17 wherein the second means operativein response to film tension includes a gear disposed concentric to thedrive shaft, second overrunning clutch means disposed between the gearand the drive shaft for coupling the gear in driving relation to theshaft when the gear is rotated in a direction corresponding to movementof film adjacent the puck toward the one sprocket, and gear meanscoupled between the drive pulley and the gear for rotating the gearabout the shaft axis at a rate less than the rate of rotation of thedrive pulley about the shaft axis.

1. Apparatus for feeding strip material in either direction through an operational zone between two storage regions comprising reversible drive means engagable with the strip material for moving the strip through the operational zone in either direction, and tension control means positioned along the path of the strip between the supply source and the drive means, the tension control means including reversible drive means engagable with the strip material for driving the strip material at a speed greater than the average speed at which the strip is moved through the operational zone in one direction and driving the strip material at a speed less than said average speed in the other direction, and means responsive to variations in the tension in the strip between one of said storage regions and the first drive means for activating the second drive means when tension in the strip exceeds a predetermined level and for inactivating the second drive means when the tension in the strip drops below a predetermined level.
 2. Apparatus as defined in claim 1 wherein the second drive means includes a rotating member adjacent the path of the strip, and said means activating the second drive means includes a pinch roller, the strip passing between the pinch roller and the rotating member, and movable means engaging the strip and movably supporting the pinch roller, said movable means responding to variations in the tension of the strip for moving the pinch roller into and out of engagement with the rotating member.
 3. Apparatus according to claim 2 wherein the means for moving the pinch roller includes a pivotable lever to which the pinch roller is mounted, and a guide roller rotatably mounted to the lever in spaced relation to the pinch roller and the lever pivot axis and defining a bend in the strip material.
 4. Apparatus according to claim 3 wherein the pinch roller is mounted to the lever between the guide roller and the lever pivot axis substantially closer to the pivot axis than to the guide roller.
 5. Apparatus according to claim 3 including means biasing the lever about its pivot axis in a direction productive of movement of the pinch roller away from the rotating member, the bias of said means being selected to define the tension level in the strip material.
 6. Apparatus as defined in claim 2 wherein the second drive means further includes a rotatable shaft to which the rotating member is mounted, a drive pulley disposed concentric to the drive shaft, and overrunning clutch means disposed between the drive pulley and the shaft for coupling the pulley in driving relation to the shaft when the pulley is driven in a direction corresponding to movement of the strip toward the operational zone.
 7. Apparatus according to claim 6 including a gear disposed concentric to the drive shaft, second overrunning clutch means disposed between the gear and the drive shaft for coupling the gear in driving relation to the shaft when the gear is rotated in a direction corresponding to movement of the strip toward the operational zone, and gear means coupled between the drive pulley and the gear for rotating the gear about the shaft axis at a rate less than the rate of rotation of the drive pulley about the shaft axis.
 8. Apparatus as defined in claim 2 wherein the second drive means includes a rotatable drive shaft to which the rotating member is mounted, means including a first overrunning clutch coupled to the drive shaft for driving the shaft in one direction at said greater speed, and means including a second overrunning clutch for limiting rotational speed of the shaft in the opposite direction to said lesser speed.
 9. In a motion picture projector having a film supply reel, an upper shuttle loop sprocket, a gate assembly which includes a frame-By-frame film advance mechanism, a lower shuttle loop sprocket and a film takeup reel disposed in serial order along a film path which traverses an optical axis of the projector with a shuttle loop defined between the sprockets, and reversible drive means connected to the reels and sprockets for moving the film in either direction between the reels, the improvement comprising film tension control means disposed nextadjacent one of the sprockets along the film path toward the adjacent reel, said film tension control means including first means operative in response to a film tension level in excess of a predetermined tension level in the adjacent film for driving the film along the path toward the one sprocket at a rate greater than the rate of film advance by the one sprocket in one direction, and second means operative in response to a film tension level in excess of a predetermined tension level in the adjacent film for braking the film along the path toward the one reel to a rate below the rate of film advance by the one sprocket in the reverse direction.
 10. Apparatus according to claim 9 wherein the film tension control means includes a rotatable film drive puck disposed proximate the film path so as to be spaced from film moving along the path when adjacent film has a tension level less than said predetermined tension level, a pinch roller disposed proximate the other side of the film path adjacent the puck, and means responsive to a film tension level in excess of said predetermined tension level for moving the pinch roller toward the puck sufficiently to cause film moving along the path to engage the puck.
 11. Apparatus according to claim 10 wherein the means for moving the pinch roller includes a pivotable lever to which the pinch roller is mounted, and a film guide roller rotatably mounted to the lever in spaced relation to the pinch roller and the lever pivot axis and defining a bend in the film path.
 12. Apparatus according to claim 11 wherein the pinch roller is mounted to the lever between the guide roller and the lever pivot axis substantially closer to the pivot axis than to the guide roller.
 13. Apparatus according to claim 11 including means biasing the lever about its pivot axis in a direction productive of movement of the pinch roller away from the puck, the bias of said means being selected to define said predetermined film tension level.
 14. Apparatus according to claim 11 wherein the film guide roller is disposed nextadjacent the pinch roller along the film path between the pinch roller and the adjacent shuttle loop sprocket.
 15. Apparatus according to claim 11 including an idler roller disposed along the film path at a fixed location between the film guide roller and the pinch roller, the film guide roller being located effectively nextadjacent the adjacent shuttle loop sprocket along the film path.
 16. Apparatus according to claim 10 wherein the first means operative in response to film tension includes means for driving the puck with a peripheral velocity of selected amount greater than the peripheral velocity of the adjacent sprocket and in a direction corresponding to movement of film adjacent the puck toward the adjacent sprocket when the adjacent sprocket is driven to supply film to the shuttle loop.
 17. Apparatus according to claim 16 wherein the puck drive means includes a rotatable drive shaft to which the puck is mounted, a drive pulley disposed concentric to the drive shaft, and overrunning clutch means disposed between the drive pulley and the shaft for coupling the pulley in driving relation to the shaft when the pulley is driven in a direction corresponding to movement of film adjacent the puck toward the one sprocket.
 18. Apparatus according to claim 17 wherein the second means operative in response to film tension includes a gear disposed concentric to the drive shaft, second overrunning clutch means disposed between the gear and the drive shaft for coupling the gear in driving relation to the shaft when the Gear is rotated in a direction corresponding to movement of film adjacent the puck toward the one sprocket, and gear means coupled between the drive pulley and the gear for rotating the gear about the shaft axis at a rate less than the rate of rotation of the drive pulley about the shaft axis. 